By default the IBM Mail sync client will only sync 30 days worth of email from your Domino mailbox. This can be changed to sync all of your mailbox by setting the server Notes.ini values below:

NTS_PRIMESYNC_TIME_LIMITS_MAIL_ENABLED=false

NTS_PRIMESYNC_TIME_LIMITS_CALENDAR_ENABLED=false

For more information and values to sync a set amount of days look at the Knowledge Center article: http://www.ibm.com/support/knowledgecenter/SSKTMJ_9.0.1/admin_imsmo/adm_controlling_mail_and_calendar_data_download.html#task_ngs_q44_yv